Precision machining operations where high precision is demanded for the workpiece make high demands for precision of the tool as well. For instance, if complicated geometries are to be formed in one milling machining step, then as a rule high speed steel (HSS) milling cutters are used, which can have a relatively complicated contour. In the production of turbine rotors, for instance, undercut slots in a rotor shaft must be made, into which correspondingly shaped roots of turbine blades are thrust. The slots have a Christmas tree profile as a rule and are undercut multiple times. The desired shape of the slot must be formed with a high degree of precision during milling.
To this end, it is known from German Patent DE 196 11 276 C1 to first open the desired slot without an undercut, and then to make the undercuts, using a milling tool equipped with indexable cutting tips, in a roughing-down machining operation. The desired precision is then attained in one or more work steps using an HSS end milling cutter. Such an HSS end milling cutter has only relatively little material to remove. Nevertheless, the feeding speed cannot be increased without limit. HSS milling cutters are inferior in terms of their cutting speed to hard-metal-equipped milling cutters.
HSS milling cutters have to be reground from time to time. In the process, especially if the outer contour of the milling cutter defines the contour of the slot to be made, the milling contour must not be changed in the regrinding. To achieve this, the tool faces are as a rule made curved adjoining the cutting edge, or in other words are provided with a radial relief. The regrinding of the HSS milling cutter is then done by regrinding the chip face, without machining the tool face. This brings about an only slight reduction in the diameter.
In most cases, the slight clearance angle necessitates machining the workpiece in synchronism. This means that the feeding direction of the workpiece essentially matches the direction of motion of the cutting edge in engagement with the workpiece. In an individual case, however, synchronized machining can cause microscopic cracks or roughness in the machined surface, which can be problematic, especially for components subjected to heavy loads.